Magnetic body



D.17,1'94e. A.F.BANDUR 2,412,668

I MAGNETIC BODY Filed Aug. 6, 1943 mmv-ron f A. 55.4 xvi/UR Arm/mm Patented Dec. 17, 1946 MAGNETIC BODY Adolph F. Bandur, Berwyn, Ill., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application August 6, 1943, Serial No. 497,675

(Cl. 26M) 2 Claims. 1

This invention relates to magnetic 'bodies comprising particles of magnetic material insulated from one another.

Magnetic bodies comprising compressed, finely divided magnetic material, in the form of dust or of assembled thin laminations of magnetic material, are extensively used as cores for loading coils, filtering coils, transformers and similar transmission apparatus in telephone and radio circuits. cults employing high frequencies and high power levels, which may cause, considerable heating of the cores, it has sometimes been found desirable Where the cores are to be used in circhanically strong. Furthermore, considerable.

precautions must be taken to insure satisfactory resistance of insulated magnetic cores to high humidities.

Objects of the present invention are to provide an effective insulation for a core made of particles of magnetic material.

In accordance with one embodiment of this invention, an insulated magnetic dust core may be formed by mixing a quantity of iron oxide powder with a water soluble soap of glycerolphthalate resin and casein and compressing and heat treating the mixture to form a core.

Other objects and advantages oi. the present invention will be more apparent from the following detailed description taken in conjunction with the single figure wherein is illustrated a magnetic core made in accordance with this invention.

In employing iron oxide powder, or other similar magnetic material, such as carbonyl iron, in the manufacture of magnetic cores, the particles of magnetic material should be individually insulated from each other and spaced a certain distance from each other in order to obtainoptimum electric and magnetic properties. At the same time, the insulating and the spacing or filling materials must not impair the temperature permeability coefficient of the magnetic core. In accordance with the present invention, the water soluble soap of glycerol-phthalate resin and casein serves two purposes: on the one hand, because of its high wetting ability, it readily forms a uniform coating of satisfactory insulating qualityover the particles of iron oxide, and, on the other hand, it also serves as a filler to provide the required spacing between the particles. The permeability temperature coefficient of cores made by using this insulating and filling material is highly satisfactory.

To form the article of this invention, a quantity of ferroso-ferric oxide of substantially chemically pure grade is passed through ado-mesh screen to remove lumps and the material is then packed in an annealing pot made of a material such as Nichrome, or other similar material which will withstand high temperatures without reacting with the oxide powder. The pot is then sealed to exclude all air and placed in a furnace heated to a temperature on the order of 1800 F. to 1860 F. The heat treatment is continued for approximately one and one-half hoursafter the material has reached the furnace temperature, and then the pot is removed from the furnace and allowed to cool to room temperature before the seal is broken. Any red oxide formed .on-the surface of the annealed powder should he rsmoved and discarded. The remaining oxide, which should be black in color, is then again passed through a lo-mesh screen to eliminate lumps which may have formed during the am healing operation.

The annealed and screened iron oxide powder is then mixed with a water soluble soap of glycerol-phthalate resin and casein, which may be previously prepared as described in the patent to Iddings 2,047,143, issued July 7, 1936. In order to thin this resin casein mixture to improve its coating characteristics, Water may be added thereto and mixed therewith to form a suspension of the required viscosity. A mixture having satisfactory coating characteristics has been formed using approximately 246 cc. of water to 35 grams of glycerol-phthalate resin and casein. A suspension of this composition and amount will satisfactorily coat grams of iron oxide powder. The amount of water to be added, however, is not critical and satisfactory coating of the particles and dispersion of the insulating material have been obtained using as little as 50 cc. of water for 100 grams of oxide powder and 35 grams of the resin casein mixture. lhe exact proportion to be used of the resin and casein mixture to the iron oxide powder is determined by the desired permeability and other electric and magnetic properties, the proportion given producing cores of highly satisfactory quality when used in accordance with the present process. It has been found in practice that this mixture does not tend aeraaea to adhereto the mixing apparatus, as is sometimes the case with other mixtures of powdered magnetic material using other insulating and filling materials, and, consequently, mixing is considerably improved and expedited.

,The iron oxide powder, the glycerol-phthalate resin and casein, and the water, are mixed in any suitable mixing device which may be heated to approximately 325 F. to cause evaporation of the water as the materials are mixed. Using the proportions of materials set forth above, under normal conditions of humidity, approximately one and one-half hours at 325 F. will be required to thoroughly mix the materials and to evaporate the water.

After the mixing operation, the mixture may be further heated at approximately 325 F. for approximately flve-l'minutes to advance the polymerization of the resin in the mixture. Care must, however, be taken that the temperature does not substantially exceed this value for any appreciable length of time in order to prevent premature curing of the resin. By partially curing the resin prior to forming the cores, such dimensional changes as are occasioned therein by the curing operation are largely completed and, when the formed cores are heated after the forma ing operation, substantially no further dimen sional changes occur. By th'us stabilizing the dimensions of the core, the magnetic and electric characteristics of the core, which are closely related, as is well known, to the size of the core,

may be accurately predetermined.

- After the mixture has been heat treated to partially cure the resin, it is then again cooled to room temperature and passed through a 30-mesh sieve. The dried and screened mixture may then be pressed into a. shape such as that shown in the 4- is largely a matter of choice, it has been found that satisfactory forming is obtained with a mixture prepared as described herein at a pressure of approximately fifty tons per square inch. It has been found that no die lubrication or dressing is required with this mixture. The formed cores .may then be baked at a temperature of approximately 410 F. to 440 F. for approximately two and one-half hoursto completely evaporate all moisture and to complete the curing of the resin. The glycerol phthalateresin and casein forms a very tight bond between the magnetic particles which has excellent mechanical strength. Fun thermore, because of the closeness of the bond, moisture is prevented from passing into the formed cores during subsequent use; the presence of moisture, of course, would tend to impair the electric and magnetic properties of the cores. The cores are'hard and may be readily handled, as maybe necessary in winding wire about the cores, and show excellent stability of permeability evenwhen usedunder high operating temperatures, such as temperatures on the order 01 '400F.'

What'is claimed is:

a .1. A magnetic body comprising particles of magnetic material insulated from one another and bonded together by the end products of a. heat-treated composition comprising a watersoluble soap of glycerol-phthalate resin and casein. 1

2.'A magnetic body comprising particles of magnetic material insulated from one another and. bonded together by the end products of a heat-treated composition comprising a waterdrawing. While the precise pressure to beused soluble soap of a glycerol-phthalate resin and casein, and an inorganic insulating filler in said composition.

ADOLPH F. BANDUR. 

